Current treatment of HIV-infected patients with combined antiretroviral therapy (cART) has provided effective suppression of virus replication, prevented immunosuppression and increased lifespan. Despite these advances, even in the presence of cART, chronic neuroinflammation cannot be fully prevented, leading to development of HIV-associated neurocognitive disorders (HAND). The above clinical observation has prompted the necessity for quantitative biomarkers to help in detection and monitoring of central nervous system (CNS) complications resulting from HIV infection. Dysfunction of the blood-brain barrier (BBB) is a well-known phenomenon in HIV-1 neuropathogenesis potentially leading to neurodegeneration. We propose novel biomarkers reflecting BBB injury, namely detection of extracelluar microvesicles (eMVs) containing tight junction proteins (TJP) released from brain endothelium. We discovered that eMV release from the brain endothelium occurs as a result of inflammation and vascular remodeling. Importantly, the same pro- inflammatory insult on brain endothelial cells (EC) induces barrier permeability and biochemical changes to tight junction complexes. This project is unique in both the development of innovative tools for biomarker discovery and identification of a novel pathophysiologic phenomenon occurring at the BBB as consequence of chronic HIV-associated neuroinflammation. In the first aim, we will profile and chronologically define the presence of TJPs in eMV secreted as a consequence of relevant inflammatory stimuli and HIV virotoxins. These determinations will be made in parallel with measurement of barrier integrity, thus allowing for correlations between eMV shedding and BBB dysfunction. Because structural proteins identify the cellular origin of the eMV, the second aim explores the notion of eMV carrying TJP as the basis for a serological biomarker for BBB dysfunction. Using the most sensitive ELISA-based available technology, we have built prototype ELISAs to measure the level of blood circulating eMVs containing TJP. Using patient serum from HIV-1 infected individuals, we provide proof-of concept results that this novel biomarker correlates with diagnosis of HAND. Experiments outlined in the third aim dissect plausible molecular mechanisms involved in the biogenesis of brain EC microvesicle formation and packaging of TJP. It will offer, not only an understanding of how eMV formation is triggered, but also will reveal targets within the cell for pharmacological intervention that promote BBB protection.